Using 12V ignition coil at 24V

I doubt it. Mine is a 1997 which was the frist (and only) year they offered this SUV with the 4-cylinder engine of the Eclipse. The ignition module is simple and cheap, looks like this:

I need to get much higher than 3600rpm.

I was thinking about actually using 12V coils here because the 24V ones are so ancient in their design and performance. I can't see what could be wrong doing that. With 24V the current ramps up twice as fast which really helps in this case but I could throttle that charge-up with a ballast resistor. If I cap at the usual 400V for flyback the coil shouldn't "feel" any difference. That was basically my question, could it experience a difference?

It's a puzzler for me as well.

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I just looked at a few Bosch ignition coils and many of them, both with and without build-in driver transistor, list dwell times for up 30V

Thanks, excellent. This one is spec'd to 24V:

Full lead-acid batteries would be 28-29V but that should be ok. I should try this one. In this case the smaller the coil the better.

P.S.: The state "Secondary resistance ... Incapable of measurement". That's a bit weird.

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the C75 is rated up to 48V

a diode in series so you can't use a regular low voltage ohm meter?

That one is on the plug, I need HV wire connected but I should be able to find one from them. It also can't be containing oil, must be fully epoxied. IOW I'll have to get one of their engineers on the phone. But thanks for the hint, Bosch should be a good contender.

Then they could run a small current through it, measure the voltage drop and deduct the diode Vf from that (which I trust they know because they picked the diode if one is in there). The rest could be done on a abacus :-)

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this one is rated for 30V and it look like the spark plug connector is optional

:-)

sure but then someone would measure it with their ohmmeter and complain it is broken

:-)

The 'diode drop' could be 60VDC. At two for a dollar, that'll take you about four bucks worth of 9V batteries for bias.

Are they really that high? The diode doesn't have to withstand the full open-plug spark voltage, only a few thousand volts to prevent sparking during charge-up.

I am sure Bosch could afford a Spellman or Kepco HV supply for their lab :-)

Yes, that one could work. It doesn't have a mounting hole but a custom bracket could be made.

A little footnote in the datasheet could prevent that. However, it is only interesting for people who want to use it "off-label" as a HV stepdown transformer and they'd also need to know whether a diode is in there.

I was taught that the original positive earth was chosen because the coil secondary could be placed on top of the primary (autotransformer), as a negative potential on the hot centre electrode required less HT, than a positive polarity, to breakdown the compressed fuel air mix.

Old fashioned? Didn't Tesla invent the CDI system? Didn't he die 75 years ago?

If CDI is the way to, one wonders why all the cars I have come across have "inductive" discharge?

Perhaps the issue is one of reliability.

I can't see petrol caring whether the spark jumps from A to B or B to A. I can imagine conduction starting more easily when the negative electrode is hot enough to emit electrons, but whether that effect really occurs I don't know. If it does, less power would then be needed. But the car still has t o start from cold, so not much saving afaics.

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That may have been true in theory but not significant enough to stop the manufacturers switching to negative ground return to reduce the issue of electrolytic corrosion effects upon the metalwork of the chassis.

You're right! I've just read the wikipedia article on CDI at this link:-

Of extreme interest to me was the reference to the Wireless World article published in March 1970 from which I built a dual points/coil variant for my T120V Triumph Bonneville. I somehow (by pure dumb luck I guess) managed to avoid the problems of winding the DC-DC converter transformer alluded to in the Wikipedia article.

Because it's a "Dirt Cheap Solution".

That's a valid point. After getting over the initial issue of the soldered joints being turned into dust by engine vibration (a 650cc parallel twin air-cooled motorcycle engine generates a lot of vibration above 3000rpm) by gluing my ersatz "PCB" (paxolin board drilled for the through hole components which were linked by the component leads and some tinned copper wire to complete the 'traces') to anchor the wired 'traces' down to the board, my biggest issue was the lack of reliability of the

Luckily, they would always fail short circuit and the topology of the circuit meant I could simply plug a spare capacitor in series between the CDI unit and the affected coil rather than resort to the indignity of reverting back to the Kettering circuit which, with the leaned out idle mixture and 40 thou gapped next grade harder plugs, would make starting a real bitch and require much higher revs and much slipping of the clutch to get under way from a standstill (you *really* did appreciate the superior sparking performance of CDI in such extremis of a complete fall back to the original Kettering setup).

I figured the problem was simply my being too cheap to choose high grade caps in the first place. I'd envisaged that the 'problematic component' would be the thyristors rather than the capacitors. It was quite surprising to discover that the 'fragile semiconductors'[1] would prove tougher than a simple passive component like a 500nF capacitor. Who knew? :-)

In this case, it was a thyristor which seems to be solid state technology's revenge on the 'cowardly fuse'. :-)

I can imagine conduction starting more easily when the negative electrode i s hot enough to emit electrons, but whether that effect really occurs I don 't know. If it does, less power would then be needed. But the car still has to start from cold, so not much saving afaics.

and many cars even back to the 2CV uses two spark plugs in series

I had one of those and I don't think they cared much about the longevity of the plugs, the main thing was that the car was cheap and somewhat reliable. With the emphasis on cheap. The less parts the better, so no distributor. I've read that spark polarity matters regarding the erosion of the spark plug's center electrode but in those days spark plugs never lasted 100000km like they do now.

I associate the polarity switchover to be associated with electronic equipment such as radios and new fangled alternators.

I made a CDI system and it was very effective compared to the original system which was marginal where the engine would occasionally miss a beat.